Carcinoids of the lung caused by exogenous noxious agents: a scoping review

Our plain-English summary of Carcinoids of the lung caused by exogenous noxious agents: a scoping review, by S. Kilo, C. Schröder, L. Frei-Stuber, et al (European Respiratory Review, 2026).

The study

• Authors: S. Kilo, C. Schröder, L. Frei-Stuber, K.H. Jöckel, D. Jonigk, F. Länger, D. Nowak
• Journal: European Respiratory Review
• Published: 2026;35(182)
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Approximately 2% of lung tumours are pulmonary carcinoids (PCs), divided into typical (90%) and atypical (AC) (10%). The link with external exposure to carcinogens remains controversial.

Objective: To investigate the association between occupational exposure to carcinogens and PC tumours.

Methods: A PRISMA-ScR-guided scoping review was performed. A systematic search was conducted in PubMed and Embase (January 2025). Studies were reviewed, data extracted, analysed and summarised narratively.

Results: 1302 studies were reviewed. 27 original studies and seven conference papers on topics including exposure to cigarette smoke (n=23) and asbestos (n=6), or mechanistic information, were included. Following the collapse of the World Trade Center in 2001, carcinoids accounted for 6% of lung cancer cases in people exposed to the resulting dust (9% in women, 3% in men). The proportion of ACs among carcinoids rose from 9.3% (controls) to 16.3% (smokers) and from ∼25% to 45% (probable versus definite asbestos exposure). Basic research has identified biological pathways linking harmful exposures (such as asbestos and cigarette smoke) to neuroendocrine cell proliferation and the potential progression of PCs to higher-grade lung tumours.

Discussion: The significance these of findings is limited due to 1) the limited number of studies, 2) the small number of tumours within those studies and 3) the lack of rigid diagnostic (morphological and molecular) criteria for PCs in most studies. Nevertheless, a consistent finding is a higher proportion of AC among carcinoids, particularly following asbestos exposure.

Conclusions: Based on these findings, a link between carcinogenic substances (especially asbestos and cigarette smoke) and carcinoids seems plausible. More stringent analyses in epidemiological surveys are needed to further clarify the pathogenesis of PCs.

Copyright ©The authors 2026.

In plain English

This article was a scoping review of published research, not a new study of patients. The authors searched PubMed and Embase for records through January 2025 on lung carcinoids, a rare type of lung tumour (about 2% of malignant lung tumours) divided into typical and atypical forms. They looked for links with substances listed as lung carcinogens in Germany's occupational disease rules. They included 27 original research articles and seven conference abstracts: six papers on asbestos, 23 on smoking or second-hand smoke, and two on World Trade Center dust. In one conference paper, 6% of lung cancer patients exposed to the dust had carcinoid tumours (9% of women, 3% of men). Three asbestos studies found that about 25% of carcinoids were atypical. In one case–control study, this rose to 45.5% among people with definite asbestos exposure. Pooled smoking data showed atypical carcinoids made up 9.3% of carcinoids in nonsmokers or very light smokers and 16.3% in smokers. The authors named lack of data as the main weakness. They concluded that a link between carcinogens (especially asbestos and tobacco smoke) and carcinoids cannot be ruled out.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Scoping review following PRISMA-ScR guidance, with a narrative (descriptive) synthesis. No meta-analysis was done and risk of bias was not assessed.
• Who was studied: Published studies, not patients. From 1302 records found in PubMed and Embase (through January 2025), plus citation tracking, the authors included 27 original research articles and 7 conference abstracts. These were published 1980 to 2024 and came from Europe, the US, Australia, China, Colombia, Israel and Turkey. They comprised 24 epidemiological studies, 6 basic research studies and 4 textbook-style or review articles.
• Exposure: Substances listed as lung carcinogens in the German Ordinance on Occupational Diseases. In practice the included studies covered active smoking or second-hand (environmental) tobacco smoke (23 publications), asbestos (6 publications, including chrysotile A, chrysotile B and crocidolite in one rat study), and dust from the World Trade Center collapse (2 conference papers).
• Main results:
  • In a conference paper on people exposed to World Trade Center dust, 6% of lung cancer patients (n=248) had been diagnosed with carcinoid tumours by the end of 2019. The figure was 9% in women and 3% in men.
  • In a rat study (Johnson et al.), animals were exposed to chrysotile A, chrysotile B or crocidolite for 26 to 104 weeks. Endocrine cells were found in their lung tissue, particularly after chrysotile B, but not in control animals.
  • In an Australian screening programme (Brims et al.), 892 asbestos-exposed people had low-dose CT scans. Six were found to have lung cancer, one of whom had an atypical carcinoid.
  • Three studies of people possibly exposed to asbestos found that 25% of carcinoids were atypical.
  • Using German mesothelioma registry data, Neumann et al. did not find an increased proportion of carcinoids among lung tumours. Among the carcinoids, however, 26% were atypical.
  • A case–control study (Clin et al.) compared 28 surgical carcinoid patients over 40 from an occupational group with possible asbestos exposure with 56 controls who had other lung cancer types. Among the carcinoid patients, 26.5% of carcinoids were atypical. Among those with definite asbestos exposure, the proportion rose to 45.5%.
  • In the same study, no asbestos exposure was found in young carcinoid patients, while 39.3% of carcinoid patients over 40 had been exposed.
  • In the authors' combined analysis of smoking studies, atypical carcinoids averaged 9.3% of carcinoids in nonsmokers or very light smokers. In smokers or heavy smokers they averaged 16.3%.
• The authors' conclusion: The authors concluded that current scientific knowledge only allows the conclusion that a link between carcinogenic substances (especially asbestos and tobacco smoke) and carcinoids cannot be ruled out. They also concluded that, for pathogenesis and occupational health and compensation questions, the data give no reason to consider carcinoids differently from other forms of lung cancer.
• Limitations the authors state:
  • The authors state that the main weaknesses were the lack of data and literature.
  • The included studies did not give enough information on possible co-exposure to different carcinogens.
  • Only one asbestos study reported the proportion of smokers.
  • Definitions of smoking exposure varied between studies, and most did not quantify it.
  • The two World Trade Center papers were conference papers that lacked many details needed to evaluate their results. The group was also intensively observed, which may indicate selection bias.
  • Accurate assessment would need typical and atypical carcinoids to be clearly distinguishable, but pathologists disagree considerably when classifying them.
  • Following scoping review guidance, the authors did not assess the risk of bias of the included studies.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Lung Cancer, Asbestos Exposure, Carcinogenic.

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